A number of physiological abnormalities manifest themselves in temperature differentials in adjacent skin areas. Trauma to the extremities cause such differentials. The trauma may involve the soft tissues with an inflammatory reaction, in which case the temperature is increased, or it may involve arteries with obliteration, in which case cooling will result. When nerves are damaged, a causalgic-like reaction is common. This may be characterized by either decreased or increased heat, depending upon whether the sympathetic nerve is irritated by the trauma (with stimulation of the nerve fibers and vasoconstriction) or if the nerve is completely severed, in which case a sympathectomy effect occurs with vasodilation.
Breast cancer is the most frequent form of fatal cancer in women and accounts for one-fifth of all female malignancies. It has been estimated that five of every one hundred women will develop breast cancer at some time during their lives. When breast cancer occurs, even with present day methods of treatment, it produces a staggering mortality, making breast cancer the number two killer of women. These deaths are even more regrettable, since the lesions give rise to lumps in an organ at the surface of the body that should easily be detected with the technology of today.
Breast carcinomas are first recognized as palpable masses by our present methods. The final diagnosis cannot be made by palpation because there are many benign breast disorders which give rise to similar masses. Benign tumors occur frequently. Consequently, the final diagnosis rests on biopsies or needle aspirations and microscopic examination. Once detected, breast carcinomas are treated by radical mastectomy and sometimes radiotherapy.
Successful treatment of breast cancer depends largely upon its stage of development at detection. If metastasis has not occurred beyond the auxiliary lymph nodes, the cancer may be completely abated. Usually, a malignant tumor cannot be recognized until it is one centimeter is diameter. Generally, regional adenopathy and dissemination do not occur at this state. However, this is not always the case, as the stage of cancer development is not directly related to the mass size. Regardness, the earliest possible diagnosis and treatment of a breast carcinoma is desirable because the possiblity of metastasis to vital areas increase with time.
Breast cancer has been observed to grow on a linear scale from the time of clinical recognition until terminal acceleration in the phases of systematic dissemination. Projection of the linear scale into the preclinical or occult stage suggests that the carcinoma has been present for many years. Therefore, there must be some symptoms available when the carcinoma is in the preclinical stage such that recognition might be feasible by combined clinical and screening techniques. The fact that cases recognized in mass screening programs are identified 21 months earlier than would be possible by clinical palpation is promising, and groups these cases in the preclinical stage.
The most widely accepted technique for early diagnosis of breast cancer is X-ray mammography. The lesion is seen as an area of increased tissue density with spotty calcifications. This technique has been used with some success. However, there are several drawbacks which have limited its use to cases in which there is a suspected carcinoma. Mammography has been of little value for the detection of breast cancer in women younger than 30 years due to the high density of the younger breast. Mammography also has practical limitations with its expense and time required by radiologists and technicians.
Thermography is the most recent method aiding in the diagnosis and screening of breast cancer. Many researchers have screened large numbers of women with and without suspicious breast characteristics using infrared radiation from the skin. The infrared emission is proportional to the fourth exponent of the temperature. A thermal pattern is recorded as a permanent black and white scan. Though IR thermography has been more successful than X-ray mammography, its application for diagnosis and screening is limited due to the high instrumentation cost.
Thermography is a method employed to map a surface temperature pattern. Ideally, a thermographic technique should give a quantitative, instantaneous thermogram equivalent to the largest possible number of individual temperature measurements per unit area with a high degree of optical resolution and sensitivity.
Cholesteric liquid crystals have unusually high thermal sensitivity. When applied to a blackened surface, these materials give rise to iridescent colors, the dominant wavelength being influenced by a very small temperature change. Liquid crystal thermography is capable of producing a thermogram over a large area with a temperature sensitivity of 0.1.degree. C and resolution of 1000 lines per inch.
Cholesteric liquid crystals demonstrate color-temperature sensitivity when in the cholesteric phase. The cholesteric phase is exhibited by many esters of cholesterol and several other organic compounds. These compounds are members of the larger class of molecular order called the mesomorphic or liquid crystalline phases. All members of this group exhibit a state of matter with an order of molecular arrangement intermediate between a true three dimensional crystal and a liquid. These compounds demonstrate the cholesteric phase within a specific temperature range, below and above which they exist as three dimensional solids and liquids, respectively.
Many efforts have been made to utilize liquid crystals in thermography of the human anatomy. For instance, the crystals have been encapsulated in natural and synthetic polymers and formed into thin sheets. This procedure does not yield a high resolution means for detecting small temperature differences because of the high heat capacities of the polymers. The heat of the body is taken up by the polymers so that the liquid crystals are not sufficiently affected to manifest small temperature differences in adjacent area segments.
Other attempts have been made to enclose liquid crystals in various kinds of polymer matrices. The products produced have not been satisfactory because of interference with the expected liquid crystal reaction by solvent contamination.
U.S. Pat. No. 3,590,371 by Hugh Shaw, Jr. layers the liquid crystal between two transparent flexible pieces of plastic. However, in this approach, no means has been provided for keeping the normally viscous, fluid liquid crystal contained between the plastic pieces, and no means has been provided for giving protection to the liquid crystal from contamination at the edges of the sandwich. Further, such a "sandwich" is delicate to handle since the two plastic pieces slip on each other with the liquid crystal acting as a lubricant.
Additionally, the liquid crystals themselves tend to flow within the package so that in some sections of the package the liquid crystal layer is thicker than in other sections. These sections, of course, have higher heat capacities than the thinner sections so that true temperature differentials on the skin surface are not faithfully recorded.
Another method in which liquid crystals have been used on the skin to detect tumors and other temperature phenomena of diseases and disorders of the body has been described in U.S. Pat. No. 3,533,399. In accordance with the procedure of the patent, the skin is coated with an application of polyvinyl alcohol and carbon black. The polyvinyl alcohol layer is allowed to dry; then a layer of liquid crystals is applied over the polyvinyl alcohol layer. The carbon black is needed to provide a sufficiently dark background to view the colors of the liquid crystal. This technique has severe limitations since the liquid crystal can only be used once. Additionally, the procedure is messy, and it is difficult to remove the polyvinyl alcohol and liquid crystal applications by washing.
U.S. Pat. No. 3,908,052 refers to a laminate which is two polymeric layers, at least the top layer being substantially transparent, sandwiching a layer of liquid crystals. The top polymer film is bonded to the bottom film in a grid pattern by heat sealing through the layer of liquid crystals. Heat sealing through liquid crystal layers is an old technique which has been employed, for example, for the preparation of novelty items in which a layer of liquid crystals is sandwiched between two polymer films and heat sealed in a selected design, for example, a bird or animal design.
Products formed by heat sealing through liquid crystals have been found generally unsuitable for temperature sensing devices requiring high sensitivity and good stability since heat sealing through the crystals contaminates them.
The procedures heretofore utilized to obtain thermograms of the human skin with liquid crystals have suffered from one or more of the following problems.
a. Heat capacity of product components other than liquid crystals is too high. PA1 b. The products are expensive to prepare. PA1 c. The products cannot be sterilized. PA1 d. The products are not sufficiently flexible to conform to the skin areas under test. PA1 e. The products do not satisfactorily protect the liquid crystals from the environment. PA1 f. The products do not provide for uniformly thin layers of liquid crystals suitable for rapid and accurate response to temperature differentials. PA1 g. The products do not have sufficient sensitivity and stability to be relied upon as a useful medical tool.